When working on the electrical wiring of a home or building, it is desirable, and necessary for safety purposes to shut off the circuit breaker supplying power to a particular electrical outlet. Circuit breaker panels typically have a plurality of circuit breakers supplying power to many areas of the home. Many times, the branches these circuit breakers control are not clearly marked, and often the markings are only general in nature. Because of the marking system employed on almost all circuit breaker panels, the person desiring to remove power to a particular branch circuit or AC power outlet usually turns off many circuit breakers in the process of trying to locate the correct one. During this trial and error period, power could be removed to other locations in the home or building not related to the branch circuit the person is trying to disable. Since the AC outlet is remotely located from the breaker panel it is difficult to know for sure that the correct circuit breaker has indeed been shut-off. It then becomes necessary to go to the remote location and check to be certain that power to the AC outlet has been removed. A test or measuring device is then required to verify that the outlet power has been properly shut off, and if it is found that the incorrect circuit breaker was selected, then another trip to the breaker panel is required. It becomes obvious that a low cost easy to use device that would allow the user to identify the correct circuit breaker from the many others in the panel would be a desirable product in the marketplace.
In the past, many methods for generating the AC line signal have been devised. A very efficient, low cost transmitter and receiver is shown in U.S. Pat. No. 4,906,938. This patent shows a simple four-component transmitter that draws short duration, fast rise time pulses of high current from the AC line. Since then many others have employed variations of this circuit to generate similar signals on the AC line. These circuit variations produce signals equal to or higher than that of the AC line frequency, and are similar to signals produced by light dimmers, which also draw fast rise time current pulses from the AC line. In some cases, these light dimmers, depending on their load, can generate signals approaching the levels of those generated by the transmitter and can be difficult to distinguish from the desired transmitter signal. In fact, most of the circuit breaker receivers developed by others will respond to the signal produced by a light dimmer even when their transmitter is not plugged into an AC outlet.
U.S. Pat. No. 4,906,938 patent also shows a simple receiver for detecting the current pulses flowing through the circuit breaker. The gain of this receiver is controlled with a user adjustable potentiometer. In order to identify the correct circuit breaker the user adjusts this potentiometer, thereby reducing the gain of the receiver amplifier, until only one circuit breaker produces a response in the receiver. Although this method of adjusting the sensitivity works quite well, first time users sometimes find it difficult to adjust this control in a timely manner.
Therefore, there is a need of a power line testing equipment that allows proper detection of signals generated by the transmitter to eliminate confusion with signals produced by other sources and facilities adjustment to the sensitivity of the receiver.